Copolylactam bowling pin

ABSTRACT

A bowling pin comprising a hollow elongated body made of a copolylactam composition containing at least 65 percent by weight polymerized caprolactam moieties, at least 1 percent by weight polymerized lactam moieties having from seven to 12 carbon atoms and N-alkyl pyrrolidone.

United States Patent [72] Inventors Thomas .I. Hyde Woodhury; Leonard A. Targonski, Pennsville, NJ. [21] Appl. No. 727,793 [22] Filed May 9, 1968 (45] Patented May 25, 1971 [73] Assignee E. I. du Pont de Nemours and Company Wilmington, Del.

[54] COPOLYLACTAM BOWLING PIN 8 Claims, 3 Drawing Figs.

[52] U.S. Cl 273/82, 260/302 [51] Int. Cl A63d 9/00 [50] Field of Search 273/82, (Dig 6); 260/324, 32.2, 30.4, 30.2

[56] References Cited UNITED STATES PATENTS 3,451,963 6/1969 Tierney 260/37 2,487,218 11/1949 Brinkman.... 273/82 2,852,485 9/1958 St0tt..... ....(2.'13/Nylon Digest) 3,012,987 12/1961 Ansul (273/82UX) 3,159,402 12/1964 Nichols 273/82 FOREIGN PATENTS 746,779 11/1966 Canada 273/82 1,058,307 2/1967 Great Britain 273/82 OTHER REFERENCES Book titled Polymer Technology Temple Press Books, 42 Russell Sq., London W.C.l., England; Article titled Polyamides by D. C. Miles & J. H. Briston; Copy in Grp. 334-273, pgs. 202-215, Nylon Digest; 1965; Lib. TP156 P6M5C2 Modern Plastics Encyclopedia Sept. 1966, Vol. 44, No. 1A, McGraw-Hill, N.Y., N.Y.; Article titled Nylons (polyamides) by L. T. Sherwood, Jr., pg. 204- 206, & 210; copy in Grp. 334, 273 Nylon Digest Primary ExaminerRichard C. Pinkham Assistant Examiner-Richard J. Apley Attorney-James J. Flynn ABSTRACT: A bowling pin comprising a hollow elongated body made of a copolylactam composition containing at least 65 percent by weight polymerized caprolactam moieties, at least 1 percent by weight polymerized lactam moieties having from seven to 12 carbon atoms and N-alkyl pyrrolidone.

65% BY WEIGHT POLYMERIZED CAPROLACTAM MOIETIES P/o BY WEIGHT LACTAM MOIETIES 0F 7 T012 OF I -5 CARBON ATOMS IN THE ALKYL GROUP.

PATENTED m2 5 IIIII 65% BY WEIGHT POLYMERIZED CAPROLACTAM CARBON ATOMS 210% BY WEIGHT OFl-S CARBON ATOMS IN THE ALKYL GROUP.

MOIETIES;I% BY WEIGHT LACTAM MOIETIES OF 7 TO I2 65 7 BY WEIGHT POLYMERIZED CAPROLACTAM MOIETIES ll BY WEIGHT LACTAM MOIETIES OF 7 TO l2 CARBON ATOMS. 2-20: BY WEIGHT N-ALKYL PYRROLIDONE PLASTICIZER OF l-5 CARBON ATOMS IN THE 5 ALKYL GROUP.

MATERIAL SELECTED FROM THE GROUP CONSISTING OF POLYMERIZED LACTAM MOIETIES I2 CARBON THEREOF.

CONTAINING 6 TO INVENTORS THOMAS J. HYDE L ONARD A. TARGONSKI COPOLYLACTAM BOWLING PIN BACKGROUND OF THE INVENTION The traditional bowling pins approved by the American Bowling Congress employ maple wood as the principal material of construction. The inevitable variability of a natural material such as wood has often led to the necessity of coring out internal portions of variable size and position within the wooden bowling pin in order to meet the specifications set by the American Bowling Congress for weight and center of gravity. In order to meet these requirements, each pin must be individually cored by nonuniform techniques in order to make these adjustments which produce a pin having the proper weight and density. This operation, as a result, is costly and inevitably leads to considerable nonuniformity in the action of the pins due to variability of the internally located cores. A further disadvantage of natural wood bowling pins is due to the fact that wood has poor recovery from deformation of the type produced by a bowling ball striking a pin, the pin striking another pin, and the pin striking the alley. During use, the wooden pin becomes increasingly pulpy and rough in the ball impact zone and hence unsuited for further use. Another disadvantage of wood is that it is not sufficiently tough to resist breakage at the most vulnerable point in the bowling pin, which is the narrow part of the neck. Breakage of the wooden bowling pin at the neck probably is the most frequent cause of early pin failure.

The consumption of maple stock for making bowling pins has increased markedly, due to the expanded popularity of bowling, and hence maple wood stock suitable for making bowling pins is gradually becoming less readily available. It is highly desirable that a suitable substitute for wood be found which is effective, readily available, uniform, economical, and more durable than maple wood. In an attempt to fill this need bowling pins fabricated from plastics have been made. However, bowling pins made of foamed or nonfoamed plastics have not become commercially successful because, among other things, some do not conform to the physical specifications of the American Bowling Congress (ABC), many do not have sonic characteristics similar to those of wood and, most importantly, available plastic pins are excessively expensive or do not have sufficient impact durability to withstand for extended periods of time, e.g., 5,000 games, the harsh treatment to which pins are subjected during bowling. Bowling pins made of polycaprolactam have been suggested, but such pins are not satisfactory, primarily because they break too readily to be an acceptable substitute for maple wood.

SUMMARY OF THE INVENTION It has now been discovered that a bowling pin comprising a hollow elongated body made of copolylactams containing at least 65 percent by weight polymerized caprolactam moieties, at least 1 percent by weight polymerized lactam moieties having from seven to 12 carbon atoms, and a plasticizing amount of N-alkyl pyrrolidone is especially resistant to damage by impact, thus giving it long life. Pins of the present invention have a proper amount of bounce or resilience that affects scoreability and have sonic qualities characteristic of wood. The pin contains a plasticizing amount, e.g. from 2 to 20 percent by weight, of N-alkyl pyrrolidone plasticizer. The bowling pin comprising a hollow elongated body can be a single wall structure, but preferably thepin has an outer shell and inner core, said shell portion externally defining said pin and preferably being integrally bonded to said core, said shell being made of copolymer of at least about 65 percent polymerized caprolactam moieties, at least about 1 percent, and usually not more than 30 percent, by weight, polymerized lactam moieties having seven to 12 carbon atoms, and a plasticizing amount, usually between about 2 and 20 percent by weight, of N-alkyl pyrrolidone. The inner surfaces of the shell or core, as the case may be, define a single cavity that extends from the head to the base section. By polymerized lactam moiety having a specified number of carbon atoms is meant a polylactam formed by the polymerization of lactam or mixtures of lactams having recurring structural units where n is 5 to l l, e.g. a polymerized caprolactam moiety has the recurring units The polymerized lactam moieties constituting the shell or core of the pin, in addition to caprolactam, are especially caprylolactam and laurolactam, although other lactams such as enantholactam, undecylonolactam, and caprilactam can be used. The N-alkyl pyrrolidone plasticizer used in the pin usually contains from 1 to 5 carbon atoms in the alkyl group, and preferably the plasticizer is N-methyl pyrrolidone. In the preferred embodiment of the pin, that is one having an outer shell and an inner core, the inner core usually is made of the same or substantially the same copolymerized composition as the shell, or it can be a homopolymer of a polylactam having polymerized lactam moieties containing six to 12 carbon atoms. In either case, the polylactam shell and core generally are integrally bonded to each other and do not separate. Various fillers, e.g. calcium carbonate, pigments, e.g. titanium dioxide, mold lubricants, mold release agents, and thickening agents may be added to the polymerizable copolylactam composition in order to, for example, color the pin, prevent settling of pigments, and to facilitate removal of the pin casting from the mold.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an external view of a copolylactam bowling pin of the present invention;

FIG. 2 is a cross-sectional view taken through the longitudinal axis of the bowling pin of FIG. 1; and

FIG. 3 is a preferred embodiment illustrating a modification of FIG. 2 showing the pin constructed of a shell and inner COI'C.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, FIGS. 1 and 2 represent a bowling pin of the present invention wherein pin 1 is a hollow elongated body contoured to define belly 2, neck 3 and head 4 sections. A copolylactam shell 5 externally defines the pin and internally defines cavity 6 having substantially the same shape as pin 1. A base perforation 7 can be made in the pin after casting. Optionally, a conventional baseplate may be attached. FIG. 3 is a longitudinal sectional view of a modified form of FIG. 1 illustrating a preferred embodiment wherein polylactam core 8 is bonded to shell 5 and has substantially the same form as the bowling pin and internally defines cavity 6. Outer shell 5 is usually thicker at belly 2, the point of ball impact. In the preferred embodiment shown in FIG. 3, the pin structure includes polylactam core 8, preferably integrally bonded to shell 5, the thickness of the core being about from one-eighth to one-fourth inches. The walls of polylactam core 8 usually have a smooth surface but, if desired, the internal and external surfaces of the core can include ribs, ridges and the like. In any event, core 8 has substantially the same shape as shell 5. The size, weight, center of gravity, and shape of the pin conform with the American Bowling Congress specifications, described in ABC Bowling Equipment Specifications, Aug. 1,

1967 edition. As mentioned above, shell of the bowling pin is made of a copolylactam composition containing at least 65 percent by weight polymerized caprolactam moieties, preferably 65 to 90 percent, 1 to 30 percent by weight polymerized lactam moieties having seven to 12 carbon atoms, and a plasticizing amount, preferably from 2 to 20 percent, of N-alkyl pyrrolidone. Preferably, the polymerized lactam moieties having seven to 12 carbon atoms are laurolactam and caprylolactam. Best results are obtained when the bowling pin is comprised of outer shell 5 and an inner core 8. The inner core is made of polymerized lactam moieties containing six to 12 carbon atoms or mixtures thereof. Most preferably, the core is made of the same, or substantially the same, copolylactam composition as the outer shell and, for added strength the polylactam core 8 also contains a plasticizing amount of N- alkyl pyrrolidone.

The bowling pins of the present invention can be prepared by polymerizing and forming two individual half shell sections of the pin, or half pins, and welding them together along the edges to form the finished pin. For example, two streams of molten caprolactam monomer each containing a lactam monomer having six to 12 carbon atoms are prepared. One of the streams contains the anionic catalyst, prepared by reacting lactam monomer, e.g. caprolactam, with sodium hydride followed by sparging with nitrogen, the anionic catalyst being the minimum ion formed during the reaction. Such anionic catalysts are well known, as illustrated in US. Pat. No. 3,207,712, and can be used in amounts of from about 0.1 to mole percent based on the total lactam in the polymerizable composition. The second stream of lactam monomer contains polymerization promoter or cocatalyst and a plasticizing amount of N-alkyl pyrrolidone. The promoters are well known, as illustrated in US. Pat. No. 3,309,343, and any promoter in amounts of from about 0.05 to 5.0 mole percent based on the total lactam in the polymerizable composition can be used in the present invention. The two streams, one containing a lactam mixture and anionic catalyst and the other containing a lactam mixture and promoter with plasticizer, are mixed and charged to a mold cavity having the shape of a hollow half bowling pin. Polymerization is conducted in the mold at a temperature, eg about 140 to 185 C., that is below the melting point of the polymer. After polymerization, two half shell sections, or half pins, are welded together by placing the edges of the half pins on a hot plate having a temperature of about 250 C. until the edges are softened, bringing the halves together edge-to-edge under pressure in a positioning jig until the united edges have solidified by cooling, thus forming the finished pin. Alternatively, the cast pin can be made by charg' ing said polymerizable lactam composition to a mold cavity having the form of a pin. The mold is heated and rotated simultaneously about its horizontal and vertical axes to distribute and polymerize the polymerizable lactam composition, leaving a cavity of the desired shape within the bowling pin. A method for making the bowling pin described in FIG. 3 having both shell and core is described in US. Pat. Application Ser. No. 727,792,. filed May 9, 1968, filed concurrently herewith, the disclosure of which is incorporated herein by reference. This application discloses forming a plastic core having substantially the same shape as the bowling pin, preferably made of copolylactam, and placing said core in a heated mold chamber, flushing the space between the core and mold cavity wall with an inert gas, filling this space in the mold cavity with a polymerizable mixture of a copolylactam composition containing N-alkyl pyrrolidone in order to form a shell about the core, pressurizing the contents in the mold cavity to at least about 10 p.s.i.g. with inert gas, maintaining said pressure until polymerization is complete thus bonding the copolylactam shell to the copolylactam core, and removing the bowling pin from the mold. When the shell is polymerized about the core, the shell generally becomes integrally bonded to the core, and

it appears that the core and shell are a single homogeneous structure, especially when the copolylactam compositions of shell and core are the same. I

A typical bowling pm of the present invention 15 made of about 78 percent polymerized caprolactam moieties, about 4 percent polymerized laurolactam moieties and about 10 percent N-methyl-2-pyrrolidone in both the shell and core. The balance may include, for example, about 4 percent Zytel 63 (i.e., a terpolymer of nylon 6, 66, and 6-10) thickening agent, 2 percent TiO pigment, 0.6 percent cocatalyst residues, 0.5 percent potassium stearate mold-release agent, 0.4 percent catalyst residues, and 0.6 percent of white mineral oil lubricant. The material of such a pin has a tensile strength of about 6,900 i 500 psi, the tensile secant modulus is about 124,000 p.s.i. at Apercent strain, and the elongation at break is about 210 percent 20 percent, all values determined by the procedures described in ASTM Method D-638. The density ofa specimen cut from the bowling pin is about 1.05 g./cc.

The bowling pins of the present invention have more than five times the useful pin life of conventional maple wood pins under similar conditions of use, and have low maintenance requirements, all of which contribute to a reduction in the operating costs of a bowling alley. in testing the bowling pins of the present invention against ABC-approved maple wood pins, it was found that the service life of the wood pins was about 1960 ball impacts whereas the preferred pins of the present invention were serviceable after 16,000 ball impacts, testing being terminated arbitrarily. Tests have shown that the bowling pins of the present invention perform in a manner substantially the same as maple wood pins in regard to scoreability so as to produce similar results game after game. The sonic qualities of the plasticized copolylactam pin are very similar to those of wood.

We claim:

1. A bowling pin comprising a hollow elongated body made of copolylactams containing at least 65 percent by weight polymerized caprolactam moieties, at least 1 percent by weight polymerized lactam moieties having from seven to 12 carbon atoms, and about from 2 to 20 percent by weight of the plasticizer N-alkyl pyrrolidone wherein the alkyl group contains one to five carbon atoms.

2. A bowling pin of claim 11 having N-methyl pyrrolidone as plasticizer.

3. A bowling pin of claim 2 having polymerized laurolactam moieties.

4. A bowling pin comprising a hollow elongated body having an outer shell and an inner core, said shell externally defining said pin and bonded to said core, said shell made of copolylactams containing at least 65 percent by weight polymerized caprolactam moieties, at least 1 percent by weight polymerized lactam moieties having from seven to 12 carbon atoms, and about from 2 to 20 percent by weight of the plasticizer N-alkyl pyrrolidone wherein the alkyl group contains one to five carbon atoms, said core having substantially the same shape as said shell and made of a material selected from the group consisting of polymerized lactam moieties containing six to 12 carbon atoms or mixtures thereof.

5. A bowling pin of claim 4 wherein the core comprises the same copolymerized lactam moieties as the shell.

6. A bowling pin of claim 5 wherein the core contains about from 2 to 20 percent by weight of the plasticizer N-alkyl pyrrolidone wherein the alkyl group contains one to five carbon atoms.

7. A bowling pin of claim 6 having about from 65 to percent polymerized caprolactam moieties, about from 1 to 30 percent polymerized lactam moieties having seven to 12 carbon atoms and 2 to 20 percent N-methyl pyrrolidone plasticizer.

8. A bowling pin of claim 7 having polymerized laurolactam moieties. 

2. A bowling pin of claim 1 having N-methyl pyrrolidone as plasticizer.
 3. A bowling pin of claim 2 having polymerized laurolactam moieties.
 4. A bowling pin comprising a hollow elongated body having an outer shell and an inner core, said shell externally defining said pin and bonded to said core, said shell made of copolylactams containing at least 65 percent by weight polymerized caprolactam moieties, at least 1 percent by weight polymerized lactam moieties having from seven to 12 carbon atoms, and about from 2 to 20 percent by weight of the plasticizer N-alkyl pyrrolidone wherein the alkyl group contains one to five carbon atoms, said core having substantially the same shape as said shell and made of a material selected from the group consisting of polymerized lactam moieties containing six to 12 carbon atoms or mixtures thereof.
 5. A bowling pin of claim 4 wherein the core comprises the same copolymerized lactam moieties as the shell.
 6. A bowling pin of claim 5 wherein the core contains about from 2 to 20 percent by weight of the plasticizer N-alkyl pyrrolidone wherein the alkyl group contains one to five carbon atoms.
 7. A bowling pin of claim 6 having about from 65 to 90 percent polymerized caprolactam moieties, about from 1 to 30 percent polymerized lactam moieties having seven to 12 carbon atoms and 2 to 20 percent N-methyl pyrrolidone plasticizer.
 8. A bowling pin of claim 7 having polymerized laurolactam moieties. 